The wedding of George and Barbara Pierce Bush, Rye, NY, January 6, 1945.

Barbara Bush wipes water off the shoulder of her husband former US president George Bush during the inauguration of the William J. Clinton Presidential Center in Little Rock, Arkansas, 18 November 2004. ROBERTO SCHMIDT/AFP/Getty Images

Vice President and Mrs. Bush attend the July 4th Parade in Wyandotte, Mich., July 4, 1988.

Former US President George H.W. Bush(L) and his wife Barbara chat at Madison Square Garden in New York City 30 August, 2004 on the first first day of the Republican National Convention. (Photo credit should read PAUL J. RICHARDS/AFP/Getty Images)

Former U.S. President George H.W. Bush and former first lady Barbara Bush attend a portrait unveiling at the George Bush Library April 21, 2003 in College Station, Texas. (Photo by Joe Mitchell/Getty Images)

George and Barbara Bush celebrate his election to Congress at campaign headquarters, 1966.

Former first lady Barbara Bush greets her husband and former U.S. President George H.W. Bush with a kiss after his successful skydive down to St. Anne's Episcopal Church on June 12, 2014 in Kennebunkport, Maine. (Photo by Eric Shea/Getty Images)

Former US President George H.W. Bush and former First Lady Barbara Bush smile as they are introduced at Bush's 80th birthday celebration at Minute Maid Stadium June 12, 2004, in Houston, Texas. (Photo by Brett Coomer/Getty Images)

Victory Night, Congressional Race, 1966

Former U.S. President George H.W. Bush (R) and his wife Barbara Bush and Florida Gov. Jeb Bush wave to the crowd on the inaugural stage January 20, 2005 in Washington, D.C. (Photo by Mark Wilson/Getty Images)

Former President George H.W. Bush and former first lady Barbara Bush stand with their son, US President George W. Bush and First Lady Laura Bush at the opening of the elder Bush's 80th birthday, June 12, 2004. Photo by Brett Coomer/Getty Images

Former U.S. President George Bush and former first lady Barbara Bush attend the swearing-in ceremony of Secret Service Director W. Ralph Basham January 27, 2003 in Washington, DC. (Photo by Alex Wong/Getty Images)

Former U.S. President George H.W. Bush and his wife Barbara applaud during the evening session of day one of the 2004 Republican National Convention August 30, 2004 at Madison Square Garden in New York City. (Photo by Justin Sullivan/Getty Images)

Former President of the United States George Bush Sr. and wife Barbara Bush attend Game Four of the 2005 MLB World Series between the Chicago White Sox and the Houston Astros on October 26, 2005. (Photo by Jed Jacobsohn/Getty Images)

George and Barbara Bush during the campaign for the Senate, 1964.

Former US President George Bush waves his program as he and his wife Barbara depart the Washington National Cathedral at the conclusion of a National Day of Prayer and Remembrance. MIKE THEILER/AFP/Getty Images

Former President George Bush and his wife Barbara walk toward the Church of Our Saviour Catholic church in September 2, 2004 in New York City. (Photo by Scott Olson/Getty Images)

Former US President George H.W. Bush and his wife Barbara applaud as their son US president George W. Bush is introduced at inaugural ceremonies 20 January, 2005 at the US Capitol in Washington, DC. DON EMMERT/AFP/Getty Images

Former President George H.W. Bush (L) and former first lady Barbara Bush wave on day two of the Republican National Convention at the Xcel Energy Center on September 2, 2008 in St. Paul, Minnesota. (Photo by Justin Sullivan/Getty Images)

Former US President George H.W. Bush and Barbara Bush walk down Pennsylvania Avenue to the White House 01 January 2007 in Washington, DC. BRENDAN SMIALOWSKI/AFP/Getty Images

US President George Bush kisses his wife Barbara at the end of a rally held at the Astro Arena on November 2, 1992 on the eve of the 1992 presidential election. EUGENE GARCIA/AFP/Getty Images

Former US president George Bush holds a garland next to his wife, Barbara shortly after arriving at a Military air base in Bangkok, 10 December 2006. PORNCHAI KITTIWONGSAKUL/AFP/Getty Images

Former President George H. W. Bush and his wife Barbara pose for photographers before the start of the 29th Annual T.J. Martell Foundation Awards Gala at the New York Hilton May 27, 2004 in New York City. (Photo by Paul Hawthorne/Getty Images)

Former President George H.W. Bush and former First Lady Barbara Bush give the thumbs-up from inside the presidential viewing stand overlooking Pennsylania Avenue during the Inaugural Parade 20 January 2005. STAN HONDA/AFP/Getty Images

US President George W. Bush and his wife Laura, stand with his parents former US President George H.W. Bush and Barbara Bush, as they leave St. John's Episcopal Church after Sunday morning services. PAUL J. RICHARDS/AFP/Getty Images

Former US President George H.W. Bush and wife Barbara take in the Houston Astros home opener against the St. Louis Cardinals on April 7, 2008 at Minute Maid Park in Houston, Texas. (Photo by Bob Levey/Getty Images)

Former U.S. President George H. W. Bush and former first lady Barbara watch as the structure of the newest aircraft carrier, the USS George H. W. Bush, is manuvered into place on the deck of ship. Photo by Gary C. Knapp/Getty Images

Former US President George Bush (L) stands with wife former US first lady Barbara Bush during presidential inaugural ceremonies for their son, George W. Bush, 20 January 2001, at the US Capitol in Washington, DC. DON EMMERT/AFP/Getty Images

US President George W. Bush and First Lady Laura Bush applaud while former President George H.W. Bush and former First Lady Barbara Bush give the thumbs-up during the Inaugural Parade in Washington, DC, January 20, 2005. STAN HONDA/AFP/Getty Images

President and Mrs. Bush walk around the south grounds of the White House prior to leaving for the inauguration ceremonies, January 20, 1993.

Former President George H.W. Bush and Barbara Bush listen as their son, US President George W. Bush, delivers the commencement address during the Texas A&M University graduation ceremony at Reed Arena on December 12, 2008.SAUL LOEB/AFP/Getty Images

President and Mrs. Bush share a laugh with Helen Thomas following the third presidential debate in East Lansing, Mich., October 19, 1992.

Former President George H.W. Bush and former first lady Barbara Bush point from their seats on day two of the Republican National Convention at the Xcel Energy Center on September 2, 2008 in St. Paul, Minnesota. Photo by Justin Sullivan/Getty Images

George and Barbara Bush on the night he was elected to Congress, 1966.

President and Mrs. Bush with Millie at Walker's Point, Kennebunkport, Maine, July 11, 1991.

Former President and Mrs. Bush share a new book in their apartment at the George Bush Presidential Library Complex, February 28, 2002.

President and Mrs. Bush arrive the train station in Burlington, Wis., October 31, 1992.

President and Mrs. Bush are interviewed in the Yellow Oval Room of the White House by Sam Donaldson and Diane Sawyer for Prime Time Live. Millie waits quietly in the background, September 21, 1989.

Former President Bush lands following a parachute jump for the 10th Anniversary and Rededication ceremonies of the George Bush Presidential Library and Museum, November 10, 2007.

Mrs. Bush examines family photographs and Millie paces the floor as President Bush works at his desk in the Oval Office, January 27, 1989.

President and Mrs. Bush participate in a tree planting ceremony on the south lawn of the White House after he signs a transmittal letter to Congress entitled "National Tree Trust Act of 1990," March 22, 1990.

President and Mrs. Bush with the Pope, Vatican City, May 27, 1989.

Mrs. Bush delivers an address at the Republican National Convention, August 19, 1992.

The wedding of George and Barbara Pierce Bush, Rye, NY, January 6, 1945.

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Barbara Bush wipes water off the shoulder of her husband former US president George Bush during the inauguration of the William J. Clinton Presidential Center in Little Rock, Arkansas, 18 November 2004. ROBERTO SCHMIDT/AFP/Getty Images

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Vice President and Mrs. Bush attend the July 4th Parade in Wyandotte, Mich., July 4, 1988.

Former US President George H.W. Bush(L) and his wife Barbara chat at Madison Square Garden in New York City 30 August, 2004 on the first first day of the Republican National Convention. (Photo credit should read PAUL J. RICHARDS/AFP/Getty Images)

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Former U.S. President George H.W. Bush and former first lady Barbara Bush attend a portrait unveiling at the George Bush Library April 21, 2003 in College Station, Texas. (Photo by Joe Mitchell/Getty Images)

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George and Barbara Bush celebrate his election to Congress at campaign headquarters, 1966.

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Former first lady Barbara Bush greets her husband and former U.S. President George H.W. Bush with a kiss after his successful skydive down to St. Anne's Episcopal Church on June 12, 2014 in Kennebunkport, Maine. (Photo by Eric Shea/Getty Images)

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Former US President George H.W. Bush and former First Lady Barbara Bush smile as they are introduced at Bush's 80th birthday celebration at Minute Maid Stadium June 12, 2004, in Houston, Texas. (Photo by Brett Coomer/Getty Images)

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Victory Night, Congressional Race, 1966

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Former U.S. President George H.W. Bush (R) and his wife Barbara Bush and Florida Gov. Jeb Bush wave to the crowd on the inaugural stage January 20, 2005 in Washington, D.C. (Photo by Mark Wilson/Getty Images)

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Former President George H.W. Bush and former first lady Barbara Bush stand with their son, US President George W. Bush and First Lady Laura Bush at the opening of the elder Bush's 80th birthday, June 12, 2004. Photo by Brett Coomer/Getty Images

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Former U.S. President George Bush and former first lady Barbara Bush attend the swearing-in ceremony of Secret Service Director W. Ralph Basham January 27, 2003 in Washington, DC. (Photo by Alex Wong/Getty Images)

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Former U.S. President George H.W. Bush and his wife Barbara applaud during the evening session of day one of the 2004 Republican National Convention August 30, 2004 at Madison Square Garden in New York City. (Photo by Justin Sullivan/Getty Images)

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Former President of the United States George Bush Sr. and wife Barbara Bush attend Game Four of the 2005 MLB World Series between the Chicago White Sox and the Houston Astros on October 26, 2005. (Photo by Jed Jacobsohn/Getty Images)

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George and Barbara Bush during the campaign for the Senate, 1964.

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Former US President George Bush waves his program as he and his wife Barbara depart the Washington National Cathedral at the conclusion of a National Day of Prayer and Remembrance. MIKE THEILER/AFP/Getty Images

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Former President George Bush and his wife Barbara walk toward the Church of Our Saviour Catholic church in September 2, 2004 in New York City. (Photo by Scott Olson/Getty Images)

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Former US President George H.W. Bush and his wife Barbara applaud as their son US president George W. Bush is introduced at inaugural ceremonies 20 January, 2005 at the US Capitol in Washington, DC. DON EMMERT/AFP/Getty Images

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Former President George H.W. Bush (L) and former first lady Barbara Bush wave on day two of the Republican National Convention at the Xcel Energy Center on September 2, 2008 in St. Paul, Minnesota. (Photo by Justin Sullivan/Getty Images)

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Former US President George H.W. Bush and Barbara Bush walk down Pennsylvania Avenue to the White House 01 January 2007 in Washington, DC. BRENDAN SMIALOWSKI/AFP/Getty Images

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US President George Bush kisses his wife Barbara at the end of a rally held at the Astro Arena on November 2, 1992 on the eve of the 1992 presidential election. EUGENE GARCIA/AFP/Getty Images

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Former US president George Bush holds a garland next to his wife, Barbara shortly after arriving at a Military air base in Bangkok, 10 December 2006. PORNCHAI KITTIWONGSAKUL/AFP/Getty Images

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Former President George H. W. Bush and his wife Barbara pose for photographers before the start of the 29th Annual T.J. Martell Foundation Awards Gala at the New York Hilton May 27, 2004 in New York City. (Photo by Paul Hawthorne/Getty Images)

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Former President George H.W. Bush and former First Lady Barbara Bush give the thumbs-up from inside the presidential viewing stand overlooking Pennsylania Avenue during the Inaugural Parade 20 January 2005. STAN HONDA/AFP/Getty Images

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US President George W. Bush and his wife Laura, stand with his parents former US President George H.W. Bush and Barbara Bush, as they leave St. John's Episcopal Church after Sunday morning services. PAUL J. RICHARDS/AFP/Getty Images

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Former US President George H.W. Bush and wife Barbara take in the Houston Astros home opener against the St. Louis Cardinals on April 7, 2008 at Minute Maid Park in Houston, Texas. (Photo by Bob Levey/Getty Images)

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Former U.S. President George H. W. Bush and former first lady Barbara watch as the structure of the newest aircraft carrier, the USS George H. W. Bush, is manuvered into place on the deck of ship. Photo by Gary C. Knapp/Getty Images

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Former US President George Bush (L) stands with wife former US first lady Barbara Bush during presidential inaugural ceremonies for their son, George W. Bush, 20 January 2001, at the US Capitol in Washington, DC. DON EMMERT/AFP/Getty Images

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US President George W. Bush and First Lady Laura Bush applaud while former President George H.W. Bush and former First Lady Barbara Bush give the thumbs-up during the Inaugural Parade in Washington, DC, January 20, 2005. STAN HONDA/AFP/Getty Images

President and Mrs. Bush walk around the south grounds of the White House prior to leaving for the inauguration ceremonies, January 20, 1993.

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Former President George H.W. Bush and Barbara Bush listen as their son, US President George W. Bush, delivers the commencement address during the Texas A&M University graduation ceremony at Reed Arena on December 12, 2008.SAUL LOEB/AFP/Getty Images

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President and Mrs. Bush share a laugh with Helen Thomas following the third presidential debate in East Lansing, Mich., October 19, 1992.

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Former President George H.W. Bush and former first lady Barbara Bush point from their seats on day two of the Republican National Convention at the Xcel Energy Center on September 2, 2008 in St. Paul, Minnesota. Photo by Justin Sullivan/Getty Images

George and Barbara Bush on the night he was elected to Congress, 1966.

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President and Mrs. Bush with Millie at Walker's Point, Kennebunkport, Maine, July 11, 1991.

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Former President and Mrs. Bush share a new book in their apartment at the George Bush Presidential Library Complex, February 28, 2002.

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President and Mrs. Bush arrive the train station in Burlington, Wis., October 31, 1992.

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President and Mrs. Bush are interviewed in the Yellow Oval Room of the White House by Sam Donaldson and Diane Sawyer for Prime Time Live. Millie waits quietly in the background, September 21, 1989.

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Former President Bush lands following a parachute jump for the 10th Anniversary and Rededication ceremonies of the George Bush Presidential Library and Museum, November 10, 2007.

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Mrs. Bush examines family photographs and Millie paces the floor as President Bush works at his desk in the Oval Office, January 27, 1989.

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President and Mrs. Bush participate in a tree planting ceremony on the south lawn of the White House after he signs a transmittal letter to Congress entitled "National Tree Trust Act of 1990," March 22, 1990.

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President and Mrs. Bush with the Pope, Vatican City, May 27, 1989.

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Mrs. Bush delivers an address at the Republican National Convention, August 19, 1992.